There are many situations in industry where it is necessary to transfer particulate material from one container to another without contamination from the atmosphere. Such a situation exists, for instance, in the art of powder metallurgy in which it is necessary to transfer raw powdered metal from its storage hopper to a mold. Exposure of the powder to air can cause oxidation of the metal particles, so that they will not enter properly into the compressing and sintering process. It is, of course, possible to shut off the transfer apparatus from the atmosphere, after the mold has been filled, by closing an air-tight valve. Such valves, however, in order to be truly air-tight must make use of seals made of an elastomer material and the fact that the metal powders are abrasive causes these seals to be quickly worn and, thus, they leak. More importantly, however, the abrasive metal particles remove particles of the elastomer material, so that the powder is contaminated. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a valve system for controlling the flow of particulate material without exposure to the atmosphere.
Another object of this invention is the provision of a valve assembly for use in transferring abrasive powders, including an air-tight valve and means for assuring that the elastomer elements of the valve are not damaged and do not contaminate this powder.
It is another object of the instant invention to provide a valve system including a primary valve for excluding air and a secondary valve for transferring material.
It is another object of the instant invention to provide a valve system for permitting the flow of powdered metal from a hopper to a mold without exposure to the atmosphere.
A still further object of the invention is the provision of a valve system permitting the flow of material without exposure to contaminating elements.
It is a further object of the invention to provide a valve system which is simple in construction, which is inexpensive to manufacture, and which is capable of a long life of useful service with a minimum of maintenance.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.